[LowerTypeTests] Mark .cfi.jumptable nounwind.

[efriedma]

Summary

It doesn't unwind, and the wrong marking leads to the creation of an .eh_frame section when it isn't necessary.

[pcc]

LGTM

[joerg]

Given that .eh_frame sections can be used to create backtraces i.e. from signal handlers, this seems to be undesirable in the generality. Shouldn't this attribute be conditional on whether functions are normally supposed to have unwind data?

[efriedma]

Are you asking about the case where -fasynchronous-unwind-tables is enabled? We normally represent that using the uwtable attribute. Not sure how we would decide whether we need the uwtable attribute; I guess we could scan the module and check if there are any other functions marked uwtable.

[joerg]

Yes, if that option is enabled explicitly or implicitly in the frontend, the expectation is that all compiler-generated functions have uwtable as well.

llvm/trunk/lib/Transforms/IPO/LowerTypeTests.cpp

void LowerTypeTestsModule::createJumpTable(
   if (JumpTableArch == Triple::arm)
     F->addFnAttr("target-features", "-thumb-mode");
   if (JumpTableArch == Triple::thumb) {
     F->addFnAttr("target-features", "+thumb-mode");
     // Thumb jump table assembly needs Thumb2. The following attribute is added
     // by Clang for -march=armv7.
     F->addFnAttr("target-cpu", "cortex-a8");
   }
+  // Make sure we don't emit .eh_frame for this function.
+  F->addFnAttr(Attribute::NoUnwind);
 
   BasicBlock *BB = BasicBlock::Create(M.getContext(), "entry", F);
   IRBuilder<> IRB(BB);
 
   SmallVector<Type *, 16> ArgTypes;
   ArgTypes.reserve(AsmArgs.size());
   for (const auto &Arg : AsmArgs)
     ArgTypes.push_back(Arg->getType());

llvm/trunk/test/Transforms/LowerTypeTests/function-arm-thumb.ll

 ; CHECK-NEXT: }
 
 ; CHECK: define private void {{.*}} #[[AA:.*]] section ".text.cfi" align 4 {
 ; CHECK-NEXT: entry:
 ; CHECK-NEXT:  call void asm sideeffect "b $0\0Ab $1\0Ab $2\0A", "s,s,s"(void ()* @f2.cfi, void ()* @g2.cfi, void ()* @h2.cfi)
 ; CHECK-NEXT:  unreachable
 ; CHECK-NEXT: }
 
-; CHECK-DAG: attributes #[[AA]] = { naked "target-features"="-thumb-mode" }
-; CHECK-DAG: attributes #[[AT]] = { naked "target-cpu"="cortex-a8" "target-features"="+thumb-mode" }
+; CHECK-DAG: attributes #[[AA]] = { naked nounwind "target-features"="-thumb-mode" }
+; CHECK-DAG: attributes #[[AT]] = { naked nounwind "target-cpu"="cortex-a8" "target-features"="+thumb-mode" }

llvm/trunk/test/Transforms/LowerTypeTests/function.ll

define i1 @foo(i8* %p) {
   ; NATIVE: sub i64 {{.*}}, ptrtoint (void ()* @[[JT]] to i64)
   ; WASM32: sub i64 {{.*}}, ptrtoint (i8* getelementptr (i8, i8* null, i64 1) to i64)
   ; WASM32: icmp ule i64 {{.*}}, 1
   %x = call i1 @llvm.type.test(i8* %p, metadata !"typeid1")
   ret i1 %x
 }
 
 ; X86-LINUX:   define private void @[[JT]]() #[[ATTR:.*]] section ".text.cfi" align 8 {
-; X86-WIN32:   define private void @[[JT]]() section ".text.cfi" align 8 {
+; X86-WIN32:   define private void @[[JT]]() #[[ATTR:.*]] section ".text.cfi" align 8 {
 ; ARM:   define private void @[[JT]]() #[[ATTR:.*]] section ".text.cfi" align 4 {
 ; THUMB: define private void @[[JT]]() #[[ATTR:.*]] section ".text.cfi" align 4 {
 
 ; X86:      jmp ${0:c}@plt
 ; X86-SAME: int3
 ; X86-SAME: int3
 ; X86-SAME: int3
 ; X86-SAME: jmp ${1:c}@plt
 ; X86-SAME: int3
 ; X86-SAME: int3
 ; X86-SAME: int3
 
 ; ARM:      b $0
 ; ARM-SAME: b $1
 
 ; THUMB:      b.w $0
 ; THUMB-SAME: b.w $1
 
 ; NATIVE-SAME: "s,s"(void ()* @f.cfi, void ()* @g.cfi)
 
-; X86-LINUX: attributes #[[ATTR]] = { {{.*}}naked
-; ARM: attributes #[[ATTR]] = { {{.*}}naked
-; THUMB: attributes #[[ATTR]] = { {{.*}}naked{{.*}}"target-cpu"="cortex-a8"
+; X86-LINUX: attributes #[[ATTR]] = { naked nounwind }
+; X86-WIN32: attributes #[[ATTR]] = { nounwind }
+; ARM: attributes #[[ATTR]] = { naked nounwind
+; THUMB: attributes #[[ATTR]] = { naked nounwind "target-cpu"="cortex-a8" "target-features"="+thumb-mode" }
 
 ; WASM32: ![[I0]] = !{i64 1}
 ; WASM32: ![[I1]] = !{i64 2}